Sanitary absorbent articles find wide and varied use in absorbing and trapping body fluids and maintaining body surfaces in a state of dryness and comfort. Such articles find use, for example in wound coverings and in sanitary protection devices. These articles generally include a liquid permeable layer which is placed nearest the body surface of the wearer and which may be an absorbent material serving as the main repository for liquid absorbed by the article. The article may be a multi-layer article having a liquid permeable layer, a separate aqueous liquid absorbing material underlying the liquid permeable layer and a liquid impermeable layer impervious to liquid absorbed into the absorbent material and serving as a protective barrier between the absorbent material and the wearer's clothing. The articles may also include an acquisition or transfer layer with a relatively open structure having a relatively high void volume for accepting and transporting the liquid to the absorbent core. The aqueous liquid absorbing material typically has a high liquid absorption capacity relative to the liquid permeable layer and transfer layer and can be made from materials such as wood pulp, creped cellulose wadding, absorbent foams and sponges, polymeric fibers, aqueous liquid absorbing polymers and combinations of these materials.
Conventional sanitary absorbent articles have an absorbent structure formed of cellulosic fibers such as cotton, wood pulp or rayon, mixtures of cellulosic and synthetic fibers such as polyethylene/polyester bicomponent fibers. These absorbent structures, in order to provide the requisite absorbency, are generally fairly thick (greater than 5 mm). The thickness of such an article can cause a high degree of wearing awareness, frequently resulting in user discomfort and/or poor fit between wearer's body surface and clothing. Although somewhat flexible and conforming to the body, thick sanitary absorbent articles frequently tend to deform or bunch in use, with further discomfort to the wearer and the possibility of loss of absorbency where it is most needed. When an article with this absorbent structure is subjected to a compressive load typically experienced in use, the structure can collapse resulting in liquid being expressed from the absorbent material and rewetting the layers through which liquid was originally routed to the absorbent structure. Since typical transfer layers and liquid permeable body surface facing layers are generally made from materials with little absorption capacity, the liquid expelled from the absorbent structure will tend to reside next to the body surface of the wearer resulting in discomfort and possible staining of the wearer's garments.
One solution to this problem utilizes aqueous liquid absorbing polymers, also known as superabsorbents, in the absorbent structure. The development of materials having a high aqueous liquid absorption capacity per unit volume has allowed the required overall thickness of absorbent articles to be reduced providing products which are less obtrusive to wear. Combination of aqueous liquid absorbing polymers with fibrous absorbents has resulted in development of absorbent articles which are relatively thin, i.e. less than 3 mm, and which generally retain absorbed fluid when subjected to compressive loads encountered in wearing the article. For example, U.S. Pat. No. 4,217,901 to Bradstreet and Roller discloses a thin sanitary napkin having a thickness from about 3.0 to about 7.0 mm and comprising a densified absorbent layer containing particulate superabsorbent.
However, when the aqueous liquid absorbing polymer is a particulate superabsorbent that is not well anchored in the absorbent structure, the particles can migrate within the structure or fall out of the article resulting in loss of absorbent capacity or variation in absorbency throughout the absorbent article. This can result in liquid and/or superabsorbent particles residing next to the body surface of the wearer; again, resulting in discomfort and possible staining of the wearers' garments.
To be most effective, an absorbent article needs to have the absorbent structure located in the region of the absorbent article where it will be most effective in absorbing and retaining liquids and the absorbent components need to be anchored within the structure.
Typically hot melt adhesives are used in the construction of an absorbent article to attach layers to one another and to adhesively fix the liquid impermeable backsheet to the liquid permeable topsheet around a peripheral edge margin to form a flange seal and thereby fully enclose the absorbent structure. Hot melt adhesives are also used in the construction of absorbent structures to laminate multiple plies together or to adhesively fix superabsorbent particles to fibrous components of the structure. Some problems encountered with absorbent-articles constructed in this way include stiffness or inflexibility of the article, hot melt adhesive blocking passage of liquid through the article to the absorbent structure and superabsorbent particles coated with the non-absorbent hot melt adhesive. U.S. Pat. No. 6,458,877 to Ahmed discloses compositions comprising at least one thermoplastic component, at least one diluent having polar functionality and at least one superabsorbent polymer. Also, European Patent Application EP-1013291 to Luizzi describes hot melt adhesives capable of absorbing liquid that are useful in construction of absorbent products and also describes an absorbent element containing hot melt adhesive comprising an aqueous liquid absorbing polymer.
There exists a need for an aqueous liquid absorbing structure, that is very thin, i.e. having a caliper less than 4 mm, very absorbent, i.e. having an absorbency greater than 5 g/g, and very flexible, i.e. having a Gurley stiffness less than 400 mg.
When the resulting absorbent article is a sanitary napkin or a pantiliner, it is freely adaptable both to the undergarment and to the body of the user. When the absorbent article is a wound covering, it is adaptable to the skin of the user and does not limit movement of the body part covered. Applicants have surprisingly discovered such a structure, which is described herein